There is known an image display apparatus that is worn on the head or face and used for viewing an image, that is, a head mount display. The head mount display includes, for example, image display units which are arranged for the respective right and left eyes and forms an enlarged virtual image of a display image by a virtual image optical system so that a user can observe an image with a realistic feeling.
The head mount display is equipped with a high-resolution display panel which includes, for example, a liquid crystal or an organic electro-luminescence (EL) element as each of the display units for right and left eyes. Further, head mount displays may be classified into a transmissive type and a light-shielding type.
The transmissive head mount display enables a wearer to observe surrounding scenery also when the wearer wears the head mount display on the head and an image is displayed thereon (refer to Patent Document 1, for example). Thus, a user can avoid the risk of, for example, collision with an obstacle when using the head mount display in the outside or during walking.
On the other hand, the light-shielding head mount display is configured to directly cover the eyes of a wearer when worn on the head, which increases an immersive feeling during viewing of an image. It is possible to duplicate a realistic feeling like viewing in a movie theater by projecting a display screen in an enlarged manner using the virtual optical system to allow a user to observe the display screen as an enlarged virtual image having an appropriate angle of view and duplicating multiple channels by a headphone (refer to Patent Document 2, for example). Further, also in the light-shielding type head mount display, there is known a video see-through method that has a built-in camera capable of capturing an image of the front side of a wearer and displays an external image obtained by the image capturing, and the wearer can observe surrounding scenery through the external image (refer to Patent Documents 3, 4, for example). Note that the former transmissive head mount display is called optical see-through or merely see-through contrary to the video see-through.
In either of the light-shielding and the transmissive types, the head mount display restricts the sense of sight and the sense of hearing of a user wearing the head mount display. In particular, the view of a user wearing the light-shielding head mount display is completely obstructed. Thus, the user cannot perform any operation to the outside such as answering a phone or input to the screen of a computer.
In the above video see-through head mount display, a view image of a user captured by a camera is displayed to allow the user to operate an object which is present in the view through the displayed image.
For example, there has been proposed a portable terminal system which is provided with a portable terminal which includes a display apparatus which performs display according to display information and a head mount display which displays a virtual screen in a display area in the view of a wearer on the basis of the display information acquired from the portable terminal (refer to Patent Document 5, for example).
However, the portable terminal system as described above is premised on that the head mount display is equipped with a camera which captures an image of the outside world. It is difficult for a user wearing a head mount display equipped with no camera to perform an operation with respect to the outside unless the head mount display is detached from the head to completely suspend viewing.